The present invention relates to a bleed valve for tapping or bleeding a portion of air from a gas turbine engine, and more particularly to a poppet for a bleed valve which provides regulated air flow to an aircraft environmental system.
It is common to bleed a portion of the inlet air from a gas turbine engine for a variety of purposes. Common purposes include providing a pressure differential on opposite sides of bearing seals to preclude oil leaks, to cool or heat components of the turbojet engine to control operational clearances, or to provide air conditioning or warm air to an aircraft cabin.
Typically, the air is tapped or bled at the gas turbine engine compressor and may be tapped between the low pressure compressor and the high pressure compressor, or from the cold air flow when the turbojet engine is of the turbo fan type. The selection of the source of the bleed air depends upon the desired temperatures and pressures of the air.
Known bleed valves may provide unstable partially open operation and are rather hard to control upon initial opening and just prior to closing. This instability results in high gain and relatively noisy operation. Such noise may be particularly disconcerting in aircraft environmental control systems which locates the bleed valve relatively close to the aircraft cockpit and passenger cabin. Further, the full open or full closed operation of known bleed valves is typically undesirable for aircraft environmental control systems in which intermediate operation is desirable for crew and passenger comfort.
Accordingly, it is desirable to provide a bleed valve assembly for a gas turbine engine which reduces leakage when closed while providing stable, controllable, and silent operation.
The bleed valve assembly according to the present invention provides a valve poppet that regulates bleed air from a gas turbine engine in a tailored manner. The valve poppet is a generally cylindrical member having a bleed portion and a base portion separated by a radially extending flange. The valve poppet is guided at both the bleed portion and the base portion to assures proper axial movement of the valve poppet and prevents rocking or yawing. The possibility of the valve poppet jamming is therefore greatly reduced.
The radially extending flange is located about the perimeter of the valve poppet to engage the valve seat on one side and receive a biasing member on the other. The flange engages the valve seat such that initial valve performance is similar to a disk valve, i.e., soft seating and very low leakage when closed.
A plurality of openings extend through the bleed portion such that partial open operation of the bleed valve assembly is particularly tailored for a desired flow. As the valve poppet moves off the valve seat, the initial gain is very low and then the gain increases steadily as more openings are exposed. The plurality of openings are preferably arrange as pairs of openings angularly separated by 180 degrees to balance side loads when the valve poppet is partially or fully open. Balanced aerodynamic side loads result in smoother and more stable operation.
The present invention therefore provides a bleed valve assembly for a gas turbine engine which reduces leakage when closed while providing stable, controllable, and silent operation.